Various solutions for providing an efficient electro-magnetic coupling between miniature transducers of cellular phones and T-coils of associated hearing aids have been suggested in the patent literature. An example of such a solution is given in US 2005/0244022.
US 2005/0244022 discloses a removable bezel for use with for example a cellular phone to enhance operation with a hearing aid. The removable bezel has an integrated electro-magnetic coil that is coupled to an audio output device of the cellular phone. The electro-magnetic coil is either inductively coupled to an acoustic transducer within the cellular phone or coupled thereto directly by direct electrical connections.
The electro-magnetic coil suggested in US 2005/0244022 constitutes an integrated part of a removable bezel and provides an enhanced magnetic field to a T-coil magnetic pick up within most conventional hearing aids.
It is a disadvantage of the arrangement suggested in US 2005/0244022 that the acoustic transducer of the cellular phone and the coil integrated in the bezel of the cellular phone are separate and discrete components. In case of a cellular phone not having an electro-magnetic coil integrated in its bezel, the bezel needs to be replaced before effective electro-magnetic coupling to a T-coil of an associated hearing aid can be achieved.
EP 1 128 705 relates to a voice coil having a flange portion protruding inward in the radial direction at an upper end portion of the voice coil whereby the voice coil takes a L-shaped cross-sectional shape. The upper end portion of the voice coil, i.e. the flange portion of the voice coil, is bonded and fixed to a central flat portion of a loudspeaker diaphragm. The increased bonding area obtained between the voice coil and the diaphragm prevents separation of the voice coil and the diaphragm.
The flange portion of the voice coil suggested in EP 1 128 705 aims purely at increasing the bonding area between the voice coil and the diaphragm. There is in EP 1 128 705 no mentioning of the dimensions of the voice coil, including its flange portion. Thus, neither the absolute nor the relative dimensions are derivable from the disclosure in EP 1 128 705. The flange portion is furthermore inwardly oriented in the radial direction and will therefore not contribute in any significant degree to increase the field strength of a radiated magnetic field so as to improve the electro-magnetic coupling to an external T-coil of an associated hearing aid.
It is an object of the present invention to provide a miniature electro-acoustic transducer offering enhanced electro-magnetic coupling to a T-coil of an associated hearing aid.
It is a further object of the present invention to provide a miniature voice coil for miniature electro-acoustic transducers, said voice coil being optimised for enhanced electro-magnetic coupling to a T-coil of an associated hearing aid.